The invention is an improved aqueous hydraulic cement slurry which is suited for use in cementing a well, particularly a well bore which penetrates a subterranean formation which produces a petroleum fluid, e.g., oil and/or gas, and/or water. The term "hydraulic cement" as used herein refers to those inorganic materials which set to a hard monolithic mass under water and include, for example, Portland, aluminous and pozzolana cements and various refinements thereof.
Hydraulic cements have been employed to improve the process of drilling wells and producing petroleum fluids therefrom. In these methods a hydraulic cement slurry is employed to cement a casing in place and also for cementing off permeable zones of permeable formations into which valuable materials may be lost. Also the cement is employed to inhibit the intrusion of aqueous fluids into the petroleum fluid producing zone of an oil or gas well. One of the desirable characteristics of an aqueous hydraulic cement slurry is that the fluid content thereof must not be readily lost to more porous medium, e.g., the geologic formation, for this causes the hydraulic cement slurry to prematurely set and thus be unsuitable in the cementing process. Various additaments, generally called fluid loss agents, have been added to hydraulic cement slurries to reduce the amount of fluid which is lost from the slurry to a permeable media. Although many different fluid loss additives have been discovered and employed many of them have other undesirable characteristics such as, for example, retarding the rate of set of the cement beyond an acceptable period of time. The present invention concerns the discovery of a fluid loss additive which provides excellent fluid loss properties while also not retarding the rate of set of the hydraulic cement slurry.